The present disclosure relates to a semiconductor memory device, and more particularly to a temperature sensing circuit capable of reducing size and current consumption and a semiconductor memory device using the same.
Generally, a volatile semiconductor memory device such as a DRAM (Dynamic Random Access Memory) is embedded in a high-speed electric system such as a personal computer and an electronic communication system and has been developed with high integration and capacity. In case of a semiconductor memory device which is embedded into a battery-operated system such as a cellular phone and a notebook computer, since a low current consumption characteristic is desperately needed, studies to reduce an operating or standby current have been steadily conducted.
A data retention characteristic of a DRAM memory cell having one transistor and one storage capacitor is very sensitive according to a temperature. Thus, it may be necessary to control an operational condition of circuit blocks according to fluctuation of the ambient temperature of a semiconductor integrated circuit. For example, in case of the DRAM used for a mobile product, a refresh period is controlled according to fluctuation of the ambient temperature. A temperature sensor, such as a DTSR (digital temperature sensor regulator) and an ATSR (analog temperature sensor regulator), is used for controlling an operational condition according to fluctuation of the ambient temperature. Such a temperature sensor performs a few operations to sense a high temperature, control an operational period to reduce current consumption in a self refresh mode and monitor the ambient temperature in a normal operation.
Meanwhile, there are semiconductor memory devices which only need to sense the high temperature among the above-mentioned operations of the temperature sensor. For example, in case of an ECC (error correction code) mobile DRAM, the only information which is monitored is whether the ambient temperature is high (about 85° C. prescribed in the specification) or not. However, conventional temperature sensors which are large in size and consume much current due to the many operational amplifiers are not appropriate for a semiconductor memory device. In this regard, there is a need for a temperature sensor, which has the function to sense the high temperature, for reduction of the size and current consumption in the semiconductor memory device.